One of the few areas that aircraft manufacturers have become fairly standardized on is warning & annunciation systems. Pretty much everybody now agrees that normal indications are represented by white or blue lettering and markings, yellow represents abnormal indications which may require attention ("caution lights"), and red indicates potentially dangerous abnormalities that must be immediately addressed ("warning lights"). Furthermore, most transport category aircraft makers have embraced the "dark cockpit" concept, which means that in normal takeoff configuration the central annunciation area should be completely dark, making any abnormalities easy to spot.
In the MegaWhacker, the annunciator panel is just below the overhead panel between the pilots, well within the normal field of vision. There are twelve red warning lights and seventy yellow caution lights, each of which have corresponding memory procedures, immediate action card items, or checklists in the emergency/abnormal book. When a caution or warning light illuminates, it is made more obvious by a flashing press-to-reset red Master Warning or yellow Master Caution light on the glareshield as well as an aural chime - three dings for warnings, one ding for caution.
It's really not uncommon to get a Master Caution. The MegaWhacker's forward baggage hold has an internal door that's right next to the lavatory door; every time passengers open the wrong door, we get a Master Caution and a "INTERNAL BAGG DOOR" caution light. The Master Caution gets the adrenaline flowing for about a half second until you look up and see it's only the bag door, and then you call the flight attendents and tell them that somebody's trying to pee on our bags. As caution lights go, it's a tame one, and it makes up the vast majority of caution lights that we see in flight.
Two weeks ago, we were descending into Boise, passing through ten thousand feet, when the Master Caution went off. We looked at the annunciator panel: "#1 ENG FADEC" was the message. At the same time, the "POWERPLANT" message appeared on the Engine Display. Something was definately up. "Number One Engine FADEC checklist, please," I called. The captain grabbed the emergency/abnormal book and thumbed through to the appropriate checklist.
This particular caution light has some notoriety at my airline. FADEC stands for Full Authority Digital Engine Control; it's a computer that regulates almost every aspect of engine operation, monitors its health, and can even shut it down for various malfunctions. If FADEC completely fails, so does your engine. There are warning lights for this, "#1 [or 2] ENG FADEC FAIL"; when it illuminates, you run the engine failure checklist on the Immediate Action Card. The yellow caution light we had, "#1 ENG FADEC," is much less serious; its checklist tells you to use caution when moving the power levers and do not use Beta range.
The notoriety comes from an incident several years back where one of our MegaWhacker captains got a FADEC caution light, failed to make the distinction between that and the warning light, and unneccessarily shut an engine down. The fallout from that incident is long and convoluted, so I won't go into it, but the #1 ENG FADEC checklist now unofficially bears his name. I doubt anyone will make that mistake again; hindsight is a wonderful thing.
In this case, I called for the appropriate checklist, it was mostly advisory in nature, and we landed without further incident. That's how caution lights generally go. They're just not a big deal if you follow the checklist. They do, however, mean that the rest of your day is probably going to be affected by maintenance. In this case it took the mechanics a few hours to find and repair the problem, resulting in the cancellation of several legs; I got a nap that felt very good since we had a 5am van time that morning.